Nature of the low-frequency noise in coherent radiation

The correction of the light intensity in one mode of a two-mode radiator oscillating at the difference frequency is calculated. The low-frequency noise is analyzed; the nature of this phenomenon is discussed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 40–43, March, 1975.The authors thanks V. L. Bonch-Bruevich for discussion of these results.     

海面波浪对海洋环境噪声垂直空间相关性的影响

研究了由海浪谱导得的噪声源的相关函数对海洋环境噪声垂直空间相关性的影响。常用的海洋环境噪声空间相关性模型一般假设海面噪声源是非相关的,这种假设可以解释一些物理现象,但是与真实情况并不符合。考虑到风成噪声与海浪运动的相关性,引入海浪谱,得到噪声源的相关函数,利用Kuperman-Ingenito (K/I)噪声模型,计算海洋环境噪声的垂直相关性。通过仿真结果与实验数据对比可以看出,在高风速下,假设噪声源不相关时计算得到的噪声场垂直相关性与实验结果相差较大,而利用由海浪谱导得的噪声源的相关函数计算得到的噪声场的垂直相关性与实验结果符合较好。     

The effect of ocean wave on the vertical spatial correlation of ocean ambient noise

The effect of the correlation function of noise sources derived from the ocean wave spectrum on the vertical spatial correlation of ocean ambient noise is investigated. The spatial correlation models of ocean ambient noise usually assume that the surface noise sources are uncorrelated. This assumption can be used to explain some physical phenomena, but it is not consistent with the real situation. Considering the relation between the ocean wave motion and the ambient noise generated by wind, the spectrum of ocean wave is introduced to calculate the vertical correlation of ocean ambient noise as the correlation function of noise sources by using the Kuperman-Ingenito(K/I) noise model. The comparison of the simulations and the experimental data shows that the simulations of vertical correlation of ambient noise have some differences with the experimental data by assuming the noise sources are uncorrelated and the simulations of vertical correlation of ambient noise have a good agreement with the experimental data by using the correlation function of noise sources derived from the ocean wave spectrum under the situation of high wind speed.     

Measurement of low-frequency noise in tunnel diodes

Conclusions Our studies have revealed that the spectral density of low-frequency current fluctuations in GaAs tunnel diodes can be described by the relation Wi(u, F)=f² (u)mF^–, where the nonlinear function f²(u) is not proportional to the rms of excess diode current. The flicker nature of the current noise in tunnel diodes derives from conductance fluctuations on the p-n junction, which occur in tunnel diodes as well as in low-noise transistors at frequencies ranging from near zero to a few kiloheriz and produce noise of almost the same absolute intensty in both kinds of devices.Leningrad Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 20, No. 5, pp. 777–784, May, 1977.     

Spatial structure of low-frequency wind noise

The distinguishing spatial properties of low-frequency microphone wind noise (turbulent pressure disturbances) are examined with a planar, 49-element array. Individual, propagating transient pressure disturbances are imaged by wavelet processing to the array data. Within a given frequency range, the wind disturbances are much smaller and less spatially coherent than sound waves. Conventional array processing techniques are particularly sensitive to wind noise when sensor separations are small compared to the acoustic wavelengths of interest.     

Model of Schottky-barrier diode low-frequency noise

A planar Schottky-barrier diode (SBD) is represented by two parallel-connected diodes that describe processes in the central region and in the leakage region. Independent fluctuations of the junction parameters and of the base resistances are sources of 1/F noise. The experimentally verified noise model developed on this basis explains the diversity of current and dependences of SBD noise observed in practice.St. Petersburg State Engineering University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 2, pp. 167–178, February, 1993.     

Acoustic diffraction tomography of the ocean

Tomographic monitoring of medium-scale inhomogeneities of the ocean using acoustic waves is considered. The basic integral equations are analyzed. A more detailed study is suggested for two patterns of diffraction tomography: pulsed translucent tomography of random inhomogeneities and hydroacoustic imaging. Some results of reconstruction of inhomogeneity images recovered based on laboratory-experiment data are presented.Institute of Applied Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 8, pp. 738–751 August, 1993.     

Time reversal of ocean noise

It has recently been shown [Roux et al., "Extracting coherent wave fronts from acoustic ambient noise in the ocean," J. Acoust. Soc. Am. 116, 1995-2003 (2004)] that the time-averaged correlation of ocean noise between two points yields a deterministic waveguide arrival structure embedded in the time-domain Green's function. By performing a set of these correlations between a vertical receive array and a single receiver, transfer functions necessary for time reversal can be extracted from ocean noise. Theory and simulation demonstrate this process and data of opportunity from the North Pacific Acoustic Laboratory experiment confirm the expected performance of a noise-based time reversal mirror.     

Impact of the device scaling on the low-frequency noise in n-MOSFETs

The impact of device scaling on modern MOS technology is discussed in terms of the random telegraph signals (RTSs) and low-frequency noise in n-MOSFETs with gradually decreased channel widths. RTSs with very large amplitude (>60%) are observed in the devices with ultra-narrow channels at room temperature for the first time. Furthermore, low-frequency noise spectra having both 1/f^' and Lorentzian type are found separately in the same ultra-narrow channel at different gate bias voltage, whereas only 1/f^' noise is observed in relatively wide channels. The observations strongly suggest that low-frequency noise in weak inversion dominantly suffer from carrier mobility fluctuation rather than carrier number fluctuation in ultra-narrow channels, which is confirmed by numerical simulations.     

Dephasing of qubits by transverse low-frequency noise

We analyze the dissipative dynamics of a two-level quantum system subject to low-frequency, e.g., 1/f noise, motivated by recent experiments with superconducting quantum circuits. We show that the effect of transverse linear coupling of the system to low-frequency noise is equivalent to that of quadratic longitudinal coupling. We further find the decay law of quantum coherent oscillations under the influence of both low-and high-frequency fluctuations, in particular, for the case of comparable rates of relaxation and pure dephasing.     

Cross-correlation in band-limited ocean ambient noise fields

Observations of ambient noise in the ocean are generally band limited, because of the natural spectral shape of the noise or the restricted bandwidth of the detection system. Either way, the noise may be regarded as white noise to which a band-limiting filter has been applied. An analysis of the two-point cross-correlation function of such filtered noise is presented for two cases, isotropic and surface-generated noise. The most pronounced effects occur with high-pass and bandpass filters when the low-frequency cut-off falls well above the first few zeros in the coherence function. In this situation, the sensor separation is very many times the longest acoustic wavelength (associated with the lowest frequency) in the passband. The filtering then produces sharp pulses at correlation delays equal to the numerical value of the acoustic travel time between the sensors. Although these pulses are narrow, they have a finite width, within which a fine structure appears in the form of multiple rapid oscillations, due to the differentiating action of the filter. The number of such oscillations increases as the low-frequency roll-off of the filter becomes steeper. This fine structure is evident in several recently published experimental determinations of the cross-correlation function of band-limited ocean ambient noise.     

Acoustic measures of low-frequency noise in extended high-frequency audiometry

A very high signal-to-noise ratio is required for equipment designed for extended high-frequency audiometry because listeners with almost no hearing ability in the extended high-frequency range may have normal hearing sensitivity in the lower frequencies. Two commercially available systems designed for pure-tone audiometry were evaluated both in the conventional and extended high-frequency range. Unwanted lower frequency signals greater than the noise floor occurred predominantly at presentation levels of approximately 110 dB SPL or higher. Test tones in the extended high-frequency range should be restricted to levels that are not associated with lower frequency noise.     

Microscopic origin of low-frequency flux noise in josephson circuits

We analyze the data and discuss their implications for the microscopic origin of the low-frequency flux noise in superconducting circuits. We argue that this noise is produced by spins at superconductor insulator boundary whose dynamics is due to RKKY interaction. We show that this mechanism explains size independence of the noise, different frequency dependences of the spectra reported in large and small SQUIDs, and gives the correct intensity for realistic parameters.     

Selection of modes from a shallow-water noise field by single bottom hydrophones for passive tomography purposes

The possibility of selecting modes that propagate between two spaced observation points without the use of vertical arrays and low-frequency emitters is considered. Modes are selected from the cross-correlation function of noise received by single hydrophones. It is shown that modes at frequencies near the minima of the dispersion dependences of their group velocities, where stationary phase regions are observed, make the main contribution to the noise cross-correlation function. This makes it possible to identify modes of different numbers and estimate their propagation times between hydrophones, which can be the basis for shallow-water passive mode tomography using data from single bottom hydrophones. The modes were selected based on data from a experiment carried out in the Barents Sea.     

Relationship between low-frequency noise and the stability of nonequilibrium structures

V. I. Lenin All-Union Electrical Engineering Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 7, pp. 885–890, July, 1989.